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Mass Transfer - Engineering

Q1:

If mass diffusivity in a mixture is equal to the thermal diffusivity, then the Lewis number is

A 0

B 1

C <1

D >1

ANS:B - 1

The Lewis number (𝐿𝑒Le) is a dimensionless parameter that relates the thermal diffusivity (𝐷𝑇DT​) to the mass diffusivity (𝐷𝑚Dm​) in a fluid mixture. It is defined as: 𝐿𝑒=𝐷𝑇𝐷𝑚Le=Dm​DT​​ If the mass diffusivity in a mixture is equal to the thermal diffusivity, then 𝐿𝑒Le would be equal to 1. So, the correct answer is: 𝐿𝑒=1Le=1